Electrically heated furnace



April 25, 1961 A.. E. MALM 2,981,820

ELECTRICALLY HEATED FURNACE Filed Sept. 16, 1959 5 Sheets-Sheet l Anders Ewart PQZWZ ig M W A ril 25, 1961 A E. MALM 2,

ELECTRICALLY HEATED FURNACE Filed Sept. 16, 1959 s Sheets-Sheet 2 Anders Eweri Ma 1m April 25, 1961 A. E. MALM 2,931,820

ELECTRICALLY HEATED FURNACE Filed Sept. 16, 1959 3 Sheets-Sheet 3 Anders we Mal 'z 5 5 United States Patent fitice 2,981,820 Patented Apr. 25, 1961 ELECTRICALLY HEATED FURNACE Anders Ewart Malm, Hallstahammar, Sweden, assignor to Aktiebolaget Kanthal, Hallstahammar, Sweden, a corporation of Sweden Filed Sept. 16, 1959, Ser. No. 840,301

Claims priority, application Sweden Sept. 20, 1958 3 Claims. (Cl. 219-35) The present invention relates to an electrically heated furnace having two or more juxtaposed tunnels or chambers in the same plane, and, if desired, having several such tunnel or chamber planes situated one above the other.

For instance, such furnaces are used for the thermal treatment of ceramic products, such as wall or floor tiles. Often they are designed as push through type furnaces. Further, furnaces of this general kind are used as hammer-furnaces, for instance. The furnaces previously proposed have been heated by means of electrical heating elements disposed horizontally, transversely to the furnace chamber, and located in closed grooves in refractory bricks, preferably between tunnel or chamber planes above and below such elements.

Heating elements composed of metallic resistance materials and having the form of corrugated bands or wire coils have been used, and higher furnace temperatures than 1250-1275" C. have not been permitted without too great a risk of overheating the elements.

However, it is desirable to work with higher furnace temperatures than has hitherto been possible, and the present invention contemplates an electn'cally heated furnace wherein such higher temperatures, viz. up to about 1600-1700 C. in air may be maintained, at the same time as other advantages are obtained.

As is known, temperatures of 1600-1700 C. can be produced by means of electric resistance elements substantially consisting of molybdenum disilicide, MoSi and the invention particularly relates to a furnace having resistance elements of this kind. However, this meets with the problem that in their practical construction elements of this kind cannot have such a great glow zone length that they could extend over such a great furnace Width as is practically used in furnaces with a plurality of juxtaposed tunnels.

Further, it has proved disadvantageous to dispose ele ments of the above-mentioned kind horizontally, when very high temperatures are concerned, because the elements may adhere to the bricks as well as because the elements and the brick materials have very diflierent expansion coefficients.

Further, for heat technical and economical reasons, a considerably higher load is applied to elements of the above-mentioned kind than to most other elements, and therefore they are not suitable for beingplaced in more or less closed notches as, in such case, their entire capacity could not be utilized.

The present invention solves these problems, and the furnace according to the invention is substantially characterized in that, there, between juxtaposed furnace tunnels or chambers are provided substantially hairpin-shaped heating elements, preferably essentially composed of molybdenum disilicide, MoSi and depending jvertically downwardly, viz. having their two terminal ends at the.

upper ends of the elements, and in that each of these elements is adapted to radiate heat by substantially free 2 radiation to the furnace tunnels or chambers on either side thereof.

- The invention will now be described in more detail with reference to the accompanying drawings which show an embodiment.

Figure 1 shows a vertical cross section of a portion of a furnace according to the invention, designed as a tunnel furnace having sixteen tunnels.

Figure 2 shows a portion of the furnace according to Fig. l in vertical longitudinal section.

Figure 3 shows a horizontal section of a portion of the furnace.

The furnace has four juxtaposed tunnels in each of the four tunnel planes A, B, C, D. Conveyor plates 2 are supported on the tunnel bottoms 3 and may be movable thereon longitudinally of the tunnels. Heating elements 5, Fig. 3, preferably of molybdenum disilicide, MoSi and having substantially the shape of a hairpin, are disposed vertically depending in rows between the furnace tunnels 1. Brick pillars 4 support the tunnel bottoms 3. v

The elements 5 are inserted and may be replaced from the vault of the furnace where they also have the terminal ends of the two lead in electrodes.

The two lead in electrodes 5b of the elements pass through corresponding holes in adaptor bricks 8 and a sealing plug 7 which is removably inserted together with the element.

The glow zone 5a of the element extends through all the tunnel planes A-D of the furnace in openings 6 and has substantially free radiation to the furnace tunnels 1.

nace for cooling electric contacts, said connection chamber has a suitably calculated superpressure of for instance a few mm. water column, for compensating the static pressure from the furnace caused by the difference in height and temperature. This is obtained by means of a suitable fan 11 connected to the connection chamber 10.

The invention is not restricted to the embodiment of a multi-tunnel furnace shown and described but may be used also in other furnaces having several juxtaposed furnace chambers.

What I claim is:

1. An electrically heated furnace having at least two juxtaposed furnace chambers in the same plane, substantially hairpin-shaped heating elements located between said chambers, said heating elements consisting substantially of molybdenum disilicide, MoSi said elements depending vertically and each having two terminals at its upper end, each of said elements being adaptedto radiate heat by a substantially free radiation to the furnace on either side thereof, a connection chamber for the connection of the heating elements situated on the roof of the furnace, said chamber having a static air pressure imparted to it which slightly exceeds pressure from the furnace caused in the furnace chambers and the brick-work of the furnace vault by the difference in height and temperature.

2. An electrically heated furnace as provided for in I 3 claim 1, wherein the furnace is provided with a plurality of the chamber planes situated one above the other.

3. An electrically heated furnace as provided for in claim 2, in which each of the heating elementshas a glow zone portion which extends through all of the cham- 5 her planes of the furnace.

4 References Cited in the file of this patent UNITED STATES PATENTS 1,776,823 Summey Sept. 30, 1930 1,803,282 Morgan Apr. 28, 1931 2,622,304 Coifer Dec. 23, 1952 

